1. Field of the Invention
The present invention relates to an image reading apparatus in which light from a light source configured with a plurality of light-emitting elements disposed in a row in a main scanning direction is irradiated toward an original, and light reflected from the original is read with a photoelectric conversion element, and also relates to an image forming apparatus provided with this image reading apparatus.
2. Description of the Related Art
In an image reading apparatus provided in an image forming apparatus such as a copy device, facsimile apparatus, or digital multifunction device, or an image reading apparatus capable of connection to a computer via a communications means such as a network, light reflected from an original that has been illuminated by a light source is read as an original image.
As an image reading apparatus, ordinarily, an image reading apparatus employing a moving original reading method in which an original is moved in order to read an original image, or an image reading apparatus employing a stationary original reading method in which an original is fixed in order to read an original image, is adopted.
More specifically, in an image reading apparatus employing the moving original reading method, an image of an original transported to one side in a sub-scanning direction is read while scanning is performed in a main scanning direction orthogonal to the sub-scanning direction using a light source that is positioned at a reading position, via a first light-transmitting plate (for example, an original reading glass). In an image reading apparatus employing the stationary original reading method, an image of an original placed on a second light-transmitting plate (for example, an original stage glass) is read while scanning is performed in the main scanning direction using a light source that moves to one side in the sub-scanning direction.
In a common configuration, a conventional image reading apparatus includes a light source unit in which a light source that illuminates an original and a first mirror are disposed, a second and a third mirror, an imaging lens, and a reducing-type image sensor such as a CCD (Charge Coupled Device) that operates as a photoelectric conversion element, and an original image is read by forming reflected light of an original that has been illuminated by the light source as an image on the image sensor from the first mirror, the second mirror, and the third mirror via the imaging lens. In another common configuration, a conventional image reading apparatus includes a light source that illuminates an original, and a contact image sensor (CIS) or the like that operates as a photoelectric conversion element, and an original image is read by reflected light of an original that has been illuminated by the light source being incident on the image sensor.
Incidentally, as the light source provided in the image reading apparatus, in some cases a light source is adopted in which a plurality of light-emitting elements are disposed in a row in the main scanning direction. Because ordinarily commercially available light-emitting elements such as light-emitting diodes (LEDs) are not supplied so as to each have the same level of luminance of emitted light, but rather have some range of luminance, ordinarily such LEDs are given a unique luminance rank according to their luminance level.
Also, when a light source in which a plurality of light-emitting elements are disposed in a row in the main scanning direction is adopted as the light source provided in an image reading apparatus, because light-emitting elements such as LEDs have directional properties that are stronger in one direction, bright spots occur on the light irradiation face of the original, and these bright spots on the light irradiation face of the original may cause uneven illuminance.
Therefore, conventionally, the image reading apparatus is designed such that uneven illuminance due to the bright spots does not occur, by specifying a luminance rank for the light-emitting elements in a range that there are no bright spot effects, or by increasing the number of mounted light-emitting elements in order to reduce the pitch of the light-emitting elements.
However, limiting the light-emitting elements by specifying a luminance rank or increasing the number of mounted light-emitting elements so that uneven illuminance due to the bright spots does not occur results in increased cost.
As a conventional image reading apparatus, there is an image reading apparatus in which in order to eliminate uneven concentration due to variation in the performance of light-emitting elements and thus prevent worsened image quality, the light amount is decreased for light-emitting elements that emit reflected light received by a light-receiving element for which the level of an output electrical signal is at least a predetermined level greater than the level of an electrical signal output by at least one of other light-receiving elements, or, in a case where there is a light-receiving element that outputs an electrical signal that is at least a predetermined level lower than a predetermined reference level, the light amount is decreased for light-emitting elements that emit the reflected light that is received by light-receiving elements other than that light-receiving element (see JP 2007-166065A).
However, with the image reading apparatus described in JP 2007-166065A, even assuming that it is possible to eliminate uneven concentration due to variation in the performance of individual light-emitting elements, it is not possible to reduce uneven illuminance due to bright spots on the light irradiation face of an original.